The enhancement of positive contrast in the magnetic resonance (MR) image of an organ rich in mitochondria, such as the liver, pancreas, or kidney, requires an agent that specifically locates in those organs and causes an increase in the longitudinal relaxation rate of water protons in those organs. The increase in the relaxation rate, which is responsible for enhancing positive contrast, is due to a dipolar interaction between the magnetic moments of the water protons and the magnetic moments of the paramagnetic contrast enhancement agent. The increase in the relaxation rate per unit concentration of paramagnetic contrast enhancement agent is called the relaxation efficiency, or relaxivity, of the agent.
Runge et al., U.S. Pat. No. 4,615,879 discloses a contrast media composition for nuclear magnetic resonance (NMR) imaging of the gastrointestinal tract. The compositions prepared in that invention provided a decrease in both the spin lattice (T.sub.1) and the spin-spin (T.sub.2) relaxation time of protons, thereby increasing the imaging of the gastrointestinal tract.
However, it would be desirable to have a composition for MR imaging which, in its native form, did not affect proton T.sub.1 and T2, that is, a composition which is substantially nonmagnetic, and which becomes a contrast agent upon in vivo administration. The present invention provides for a MR imaging composition for MR imaging of organs such as the liver.